1. Technical Field of the Invention
The present invention pertains in general to switching mechanisms for selectively connecting either a power output amplifier or a low noise input amplifier of a transceiver to an antenna and, more particularly, to an antenna switch capable of operation at high frequencies which selectively connects differential signals of either a power output amplifier or differential signals of a low noise input amplifier of a radio transceiver to an antenna.
2. Description of Related Art
When connecting a single antenna to a radio transceiver, a mechanism is required to selectively connect a transceiver output to the antenna while isolating a transceiver input from the antenna during transmissions and selectively connect the transceiver input to the antenna while isolating the transceiver output from the antenna during receptions. In the past, input and output signals from the transceiver have typically been designed in a single-ended fifty ohm environment with various methods available for providing the switching functionality. For example, a Field Effect Transistor (FET) is incorporated onto a single pole double throw circuit configuration to selectively connect the single-ended signals to the antenna depending on whether the transceiver is transmitting or receiving.
Although Field Effect Transistors in a single pole mechanisms are capable of incorporation onto a single integrated circuit chip along with the transceiver, their operation is limited to relatively low frequencies. Operation at higher frequencies typically requires the use of a discrete PIN diodes or expensive Gallium Arsenide transistors to perform the switching function. For example a commonly known technique uses a PIN diode in combination with a quarter wavelength transmission line to selectively transform a short circuit to an open circuit and vice versa for selectively connecting and disconnecting the antenna to either the power output amplifier or the low noise input amplifier of the transceiver.
Today, there are increased demands to reduce the size of radio equipment particularly in the radio telephone industry. To reduce the size of the radio equipment, more and more functionality is being incorporated onto a single integrated circuit chip. As more functionality is integrated onto a single integrated circuit, however, interference between different functional blocks increases. To reduce the interference, signals running between components are routed as differential signals rather than single-ended signals. Therefore, to incorporate an antenna switch "on-chip" a mechanism for connecting a differential output signal pair of the power output amplifier and a differential input signal pair of the low noise amplifier to a single-ended signal of the antenna is required. Moreover, the antenna switch needs to operate at relatively high radio frequencies used by many radio telephones found today and to appear in the future. These radio frequencies can be in excess of two gigahertz.
It would be advantageous, therefore, to devise an antenna switch for selectively connecting a differential output signal pair of a power output amplifier and a differential input signal pair of a low noise input amplifier of a transceiver to a single-ended signal of an antenna. It would further be advantageous if the antenna switch operated at frequencies above two gigahertz and was capable of integration onto a single integrated circuit chip, particularly a Bipolar Complementary Metal Oxide Semiconductor, with the transceiver. It would still further be advantageous if the antenna switch was inexpensive to fabricate.